This application claims the benefit of Korean Patent Application No. 2001-68631, filed Nov. 5, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing an ink-jet printhead, and more particularly, to a method of manufacturing a monolithic ink-jet printhead using a negative photoresist.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined color image by ejecting a small volume of a droplet of ink at a desired position on a recording sheet. In these ink-jet printheads, the ink is supplied to an ink chamber from an ink reservoir via an ink feed hole and a restrictor. The ink filled in the ink chamber is heated by a heating element provided in the ink chamber and is ejected in a droplet shape through nozzles by a pressure of bubbles generated by the heating element.
In general, the ink-jet printheads require a structure in which a number of nozzles are highly integrated, as the ink-jet printheads realize high resolution and high speed printing. In this case, a shape and precision of each nozzle and uniformity and precision between cells of the ink passage are the most important process variables for improving printing performances and realizing high quality images.
FIGS. 1A through 1H are cross-sectional views illustrating a conventional method of manufacturing an ink-jet printhead using a roof shooting method. Basically, a photolithography process and an electro forming process are used in the method of manufacturing the ink-jet printhead using the roof shooting method.
The method of manufacturing the ink-jet printhead using the roof shooting method includes manufacturing a nozzle plate 15 as shown in FIGS. 1A through 1D, forming an ink passage including an ink feed hole 22, a restrictor 27, and an ink chamber 26 on a head chip substrate 21 on which a heating element 23 is formed as shown in FIGS. 1E through 1G, and attaching the nozzle plate 15 to the head chip substrate 21 to complete the ink-jet printhead as shown in FIG. 1H.
More specifically, a seeding layer 12 for the electro forming process is formed on a silicon substrate 11 as shown in FIG. 1A, and positive photoresist 13 is coated on the seeding layer 12. That is, the seeding layer 12 is formed to a thickness of several thousand xc3x85 by sputtering or depositing NiV on the silicon substrate 11. The positive photoresist 13 is coated to a thickness of about several xcexcm, i.e., usually to a thickness between 4 xcexcm and 8 xcexcm, through spin coating. Subsequently, the positive photoresist 13 is selectively exposed to a beam hv using a photomask 14.
Subsequently, the exposed photoresist 13 is developed. In this case, only a remaining photoresist 13a of an unexposed portion of the positive photoresist 13 remains on the seeding layer 12 as shown in FIG. 1B. A crater 15b will be formed by the remaining photoresist 13a around a nozzle 15a shown in FIG. 1D.
FIG. 1C illustrates a case where the nozzle plate 15 of nickel is formed on the seeding layer 12 by soaking the patterned substrate 11 in a plating container and performing the electro forming process. In this case, the nozzle plate 15 can be formed to a desired thickness by adjusting a total current density and a plating time applied to the plating container. Simultaneously, plating is suppressed on the remaining photoresist 13a, and thus the nozzle 15a is formed.
After the electro forming process is completed, the nozzle plate 15 is separated from the substrate 11 and is cleaned as shown in FIG. 1D. In this case, the crater 15b is formed by the remaining photoresist 13a around the nozzle 15a. 
FIG. 1E illustrates a case where a negative photoresist 24 is coated on the head chip substrate 21 on which the heating element 23 formed of a resistance heating body and the ink feed hole 22 are formed. The negative photoresist 24 is coated on the head chip substrate 21 by a lamination method of heating and pressurizing and compressing a dry film resist of resin, such as VACREL or RISTON manufactured by DUPONT, on the head chip substrate 21.
Subsequently, the negative photoresist 24 is selectively exposed to the beam hv using a second photomask 25 as shown in FIG. 1F. As a result, an exposed portion of the negative photoresist 24 is cured, and a barrier wall 24a surrounding the ink chamber 26 is formed as shown in FIG. 1G. An unexposed portion of the negative photoresist 24 is removed using solvent, and thus the ink chamber 26 and a restrictor 27 are formed. The restrictor 27 is a connection path formed between the ink feed hole 22 and the ink chamber 26.
Last, the previously-manufactured nozzle plate 15 is heated and pressurized on the barrier wall 24a and is attached to the head chip substrate 21, thereby the ink-jet printhead is manufactured as shown in FIG. 1H.
The above-mentioned method of manufacturing a nozzle plate is well known as a Mandrel type nozzle electro forming method. At present, many manufactures employ the method in manufacturing a color ink-jet printhead and a mono ink-jet printhead having a small number of nozzles.
However, the method shown in FIGS. 1A through 1H causes many problems as the integration of a cell marked by cell per inch (CPI) and the number of the nozzles 15a increase. First, since the nozzle plate 15 should be separately manufactured and attached to the head chip substrate 21, high precision is necessary in this process. Second, misalignment between the nozzle 15a and the heating element 23 may occur because thermal expansion coefficients of the nozzle plate 15 and the head chip substrate 21 are different from each other when the nozzle plate 15 is heated and attached to the head chip substrate 21. Third, since one electro forming process, two photolithography processes, and one adhesion process should be performed, a process of manufacturing the ink-jet printhead becomes very complicated.
Accordingly, another method of manufacturing the ink-jet printhead by monolithically forming elements, such as the ink passage and the nozzle, on the head chip substrate has been recently introduced.
FIG. 2 is a perspective view of a conventional ink-jet printhead using a side shooting method, and FIGS. 3A through 3E are cross-sectional views illustrating a method of monolithically manufacturing the ink-jet printhead shown in FIG. 2. Drawings on the left side of FIGS. 3A through 3E are cross-sectional views taken along line Axe2x80x94A of FIG. 2, and drawings on the right side of FIGS. 3A through 3E are cross-sectional views taken along line Bxe2x80x94B of FIG. 2. A photolithography process is basically used in the method, but the electro forming process and the adhesion process are not used in this method.
Referring to FIG. 2, the conventional ink-jet printhead using the side shooting method has a structure in which an ink passage forming wall 41 forming an ink feed hole 45, an ink chamber 42, and an ink passage 43 are stacked on a head chip substrate 31. A heating element 32 is formed at one side of the ink passage 43, i.e. in a portion adjacent to the ink chamber 42, and a nozzle 44 is formed at the other side of the ink passage 43.
The method of monolithically manufacturing the ink-jet printhead having the above structure will be described stepwise below.
A positive photoresist 33 is coated to a thickness of about several ten xcexcm on the head chip substrate 31 on which the heating element 32 of a resistance heating body is formed as shown in FIG. 3A. Subsequently, the positive photoresist 33 is selectively exposed to a beam hv using a photomask 34.
Next, the exposed photoresist 33 is developed. In this case, only a remaining photoresist 33a of an unexposed portion of the positive photoresist 33 remains on the head chip substrate 31 as shown in FIG. 3B. The ink chamber 42 and the ink passage 43 shown in FIG. 2 will be formed by the remaining photoresist 33a. 
Next, a photocurable polymer 34 cured by heat or light is coated on the head chip substrate 31 and the remaining photoresist 33a as shown in FIG. 3C. Subsequently, if ultraviolet (UV) is flush exposed to (radiated on) the photocurable polymer 34 as shown in FIG. 3D, an exposed portion of the photocurable polymer 34 is cured, and thus an ink passage forming wall 41 is formed. A portion of the remaining photoresist 33a is exposed to an outside of the ink passage forming wall 41 by cutting the ink passage forming wall 41 of FIG. 3D along line Cxe2x80x94C of FIG. 3D.
Referring to FIG. 3E, if the remaining photoresist 33a is dissolved using solvent, the ink chamber 42, the ink passage 43, and the nozzle 44 are formed. Meanwhile, the ink feed hole 45 is formed before the remaining photoresist 33a is removed using solvent. As a result, the ink-jet printhead using the side shooting method shown in FIG. 2 is manufactured.
The above-mentioned method of manufacturing the ink-jet printhead is a method of monolithically forming the ink passage and the nozzle on the head chip substrate. Accordingly, in absence of the electro forming process and the adhesion process, the method might have an advantage that a process simpler than that of the method shown in FIGS. 1A through 1H is performed. In addition, since the ink passage, the nozzle, and the heating element are aligned by the photolithography process, the misalignment might not occur, and thus the uniformity between cells and the printing performances might be improved. However, there is a limit in manufacturing the ink-jet printhead since the method can be implemented only in the ink-jet printhead using the side shooting method. Further, since the method requires a cutting process, the nozzle and the ink passage may be clogged by dust and particles occurring in the cutting process, and the shape of the photocurable polymer for forming the ink passage may be deformed during the cutting process.
To solve the above and other problems, it is an object of the present invention to provide a method of forming a monolithic ink-jet printhead having an improved structure in which elements, such as a nozzle and an ink passage, are monolithically formed on a substrate using a single negative photoresist and thus a process of manufacturing the ink-jet printhead is simplified.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, there is provided a method of manufacturing a monolithic ink-jet printhead in which an ink passage, which supplies ink from an ink reservoir to an ink chamber, and a nozzle, through which the supplied ink is ejected, are monolithically formed on a substrate. The method includes forming a heating element, which generates bubbles by heating ink, on a surface of the substrate, coating a negative photoresist to a predetermined thickness on the substrate on which the heating element is formed, first exposing the negative photoresist to light by flush exposing to cure a portion, which forms a sidewall of an ink passage forming wall surrounding the ink chamber and a restrictor, of the negative photoresist using a first photomask in which patterns of the ink chamber and the restrictor of the ink passage are formed, second exposing the negative photoresist to the light by exposing a portion, which forms an upper wall of the ink passage forming wall, of the negative photoresist to cure the portion to only a predetermined second thickness using a second photomask in which a pattern of the nozzle is formed, and dissolving and removing an uncured portion of the negative photoresist using solvent in the first exposing and the second exposing.
When the negative photoresist is a dry film resist, etching the substrate to form an ink feed hole is performed between the forming of the heating element and the coating of the negative photoresist. When the negative photoresist is a liquid, etching the substrate to form the ink feed hole is performed between the second exposing and the removing of the uncured portion from the negative photoresist.
According to the present invention, the ink-jet printhead whose elements are monolithically formed by a simplified process using a single negative photoresist can be manufactured. Also, when the substrate is a silicon wafer, this is effective in mass production.
In the forming of the heating element, the heating element is formed on the substrate by sputtering metal as a resistance heating body or by depositing an impurity-doped polysilicon layer through chemical vapor deposition and patterning the impurity-doped polysilicon layer.
It is possible that the negative photoresist includes at least one selected from a group of epoxy-family, polyimide-family, and polyacrylate-family, and the coating thickness of the negative photoresist is between 10 xcexcm and 100 xcexcm.
It is also possible that when the negative photoresist is the dry film resist, the negative photoresist is coated on the substrate through lamination, and when the negative photoresist is the liquid, the negative photoresist is coated on the substrate through spin coating.
It is also possible that a dose in the first exposing is between 1000 mJ/cm2 and 4000 mJ/cm2, and the dose in the second exposing is between 2 mJ/cm2 and 300 mJ/cm2. Here, heights of the ink passage and the nozzle are adjusted by the dose in the second exposing.